I made a gist based on Sam's previous work:
https://gist.github.com/versioncontrol/7013685
```
Rehearsal --------------------------------------------------------
without_delete         2.020000   0.020000   2.040000 (  2.041702)
with_delete            2.010000   0.020000   2.030000 (  2.033683)
with_keys              1.970000   0.020000   1.990000 (  1.987906)
with_keys_start_with   0.290000   0.000000   0.290000 (  0.297689)
orig                   0.100000   0.000000   0.100000 (  0.100204)
----------------------------------------------- total: 6.450000sec

                           user     system      total        real
without_delete         1.930000   0.010000   1.940000 (  1.949233)
with_delete            1.890000   0.020000   1.910000 (  1.908764)
with_keys              1.880000   0.020000   1.900000 (  1.900992)
with_keys_start_with   0.250000   0.000000   0.250000 (  0.251627)
orig                   0.080000   0.000000   0.080000 (  0.085665)
```

Based on this, deleting it doesn't make a huge difference. But I made a mistake using regex, instead of ``` start_with? ```, which makes the filter much faster.